Satellite digital audio radio service (SDARS), a satellite broadcast service established by the U.S. Federal Communications Commission (FCC), has been proposed using satellite transmission of digital audio programs to radio receivers. The radio receivers can be stationary receivers (i.e., with a receiver antenna pointed for optimal line of sight (LOS) reception from a satellite) or mobile receivers (e.g., a receiver that is hand-carried by a user or is mounted in a vehicle).
A programming center 20 for SDARS can provide different types of programs such as music programs (e.g., jazz, classical, rock, religious, country, and so on) and news programs (e.g., regional, national, political, financial and sports) for transmission via satellite(s). The SDARS can also provide emergency information, travel advisory information, educational programs, and the like. These programs are generally time division multiplexed into a composite data stream with other information such as overhead information (e.g., data for framing, synchronization and service layer headers).
It would be advantageous to provide receivers in digital broadcast systems in general, and particularly mobile satellite receivers in vehicles, with information such as software updates for engine operation, user information such as updated maps and local weather and traffic reports, and the like. This information, however, is likely to consist of relatively large files which would require large amounts of bandwidth of the digital broadcast system to transmit in a short period of time. As the primary application for the SDARS service is the transmission of broadcast programs, it is not preferred to take large amounts of bandwidth away from the broadcast programs to support file transfer applications. Accordingly, a need exists for transfer of data to receivers in a digital broadcast system which minimizes the impact on system bandwidth requirements for transmitting other broadcast programs.
File transfers between devices in two-way communication systems (e.g., packetized transmission between network computers using a protocol such as TCP/IP) are facilitated by the ability of the devices to acknowledge successful transmission of packets and to request retransmission of those packets that were not successfully received. Digital broadcast signals, however, generally do not have a back channel with which a receiver can inform the broadcast station that part of a file was not successfully received. In co-pending U.S. patent application Ser. No. 09/695,315, a satellite receiver in a vehicle operates in conjunction with a cellular telephone to provide a back channel for such revenue-generating communications as transmitting GPS coordinates to a vehicle fleet operations control center. File transfer messaging (e.g., transmission acknowledgments and retransmission requests) is not a cost-effective use for such a back channel.
In addition, mobile satellite receivers can be subject to service outages from loss of line of sight reception due to physical obstructions, as well as from interference. Mobile satellite receivers are also turned off for periods of time when the vehicle is not in use. Accordingly, a need exists for a file transfer mechanism in a digital broadcast system which does not require a back channel between the receiver and the broadcast station and which provides means for overcoming data loss due to obstructions, interference or other interruptions during file transfer such as interruptions in vehicle use.